I've been working on a large project for a few months now. It's a DC power distribution unit, and as you can imagine it has need for relays. I've got the thing setup to accept cards to can perform many uses both input and output. One of the many cards I've designed for this system (dual low-side switching relay, 5V, 12V, audio sensor etc..) is a dual high-speed 12V solid state relay card.

Rendering of PDU and fresh pile of PCBs from Circuitmart

This is a photo of the relay on a breadboard.

single channel of dual high-speed 12V solid state relay on breadboard

This is the card from both sides. The "empty" space is used for thick and wide traces to carry current. These will be built with 6oz copper and can source 23A @ 330W in theory. I've only pushed them to 100W so far but they showed no meaningful rise in temperature so I think I am on the right track. By the numbers, they are right where they should be.

Because these cards are small and parts count it large (4 diodes, 6 transistors, a driver IC, 7 resistors, 1 tant cap) I sourced ICs with the configs I needed inside of them pre-configured. You would be amazed what you can find at Digikey if you look hard enough. Anyway, I'd never used these ICs before so I was required to design the footprints for them and lay them all out and what not. Long story short (too late), I read the datasheet wrong for one of them and got some pins confused. I didn't notice this until I had it all built up and my beautiful square wave looked like this.

Not so square... :(
I began going through everything and I found the problem, but what to do? Well, run new wires of course!

I didn't have to do any drilling because I happened to have vias available so I just needed to cut some traces and thread some wire. I used an old length of stranded telephone wire. After stripping the outer shield, I removed one of the four insulated wires inside and stripped it down to its constituent 8 strands. I used two strands (twisted) for the short trace and one strand of the longer one. In order to raise the single strand's current capacity a bit, I wet the entire length of the strand with solder. This also stiffens it so it wont bend so easy.

I found myself needing a 480W power supply to test a high current project I was working on. A 500W bench/lab power supply will set you back $100s so I figured a PC power supply was the cheapest bet. For $80 you can get a Wonhunglow brand. I checked ebay and found Dell 500W server power supplies CHEAP. Like $2 cheap.

I acquired a couple and figured out how to turn the thing on by shorting 3 pins together. Then I designed a simple little 4 rail power supply PCB and had it built by OSH Park. This power supply outputs 12V and 5V and 4V. I didn't have any use for the 4V so I skipped those pins but did add a 500mA 3.3V LDO to my board so I have 3.3V, 5V, 12V, and GND rails available. I left a large section of the solder mask missing so I could solder on some more current carrying capacity and called it done. I used a DPDT switch to short out the 3 pins required to turn on the 12V rail and added a little LED to indicate that the 3.3V regulator was running and put a small current limiting resistor on the LED so that the regulator is stabilized (I didn't check the datasheet too closely but it is common for an LDO to behave strangely until it has a minimum load). One minor complicating factor was the unusual connector on this hot swappable power supply. It had a part number on it though and I was able to get Molex to send me a couple mating adapters.

I will redesign this with a fully adjustable constant voltage and constant current output in the the future. That will be a bit of a project because 500W is a lot of power to bleed off and I want it to be accurate so I plan to use 12bit DACs and ADCs. I've been looking around for them and they are expensive enough that I think I will just use a ARM Cortex 3 microcontroller with on board 12 bit converters. More on that on some future post.

A little over 2 weeks ago, we at Freeside Atlanta launched a series of classes on Meetup on everything from Linux to 3D Printing. They've been a huge success so far! Our 3D Printing class, shown above, was taught by 3D Printing Expert Anthony Aragues. We had 11 students sign up for the first class, where they covered the recent iterations of hardware and software and how to use them.

In fact, every single class that we launched filled to capacity. Intro to Linux, Intro to Electronics, Intro to Arduino, CNC, and 3D printing. Thank you to all of the Teachers and Students that made this little experiment such a success! Because of how well this first round went we'll be launching more classes and workshops soon, so stay tuned!

I've got a little reflow oven simulation running on the LCD. I think its going to be great for the reflow oven project.

The source for the sketch in the video is attached below. The library now does vectors in addition to text and bitmaps. I am now extending the Adafruit GFX library so I can use those vector drawing routines in addition to my PGM space bitmaps. I still need to clean up the unnecessary banging I am doing on one pin. I'll post up the code on the interwebz for all to use once that is cleared up. I need a darn oscilloscope to inspect that pin!

If you need an early copy of the library and you don't know how to contact me, PM me from the youtube video.

If any of you guys were at Freeside this weekend, you would have seen me staring into the oscilloscope trying to make heads or tails of its output and comparing that to a couple of datasheets. One of those datasheets was for the Atmega328P microcontroller that is on the Arduino UNO, the other was the Sharp Memory LCD. These are cool because the are ultra low power 6uW and have extremely high contrast.

The Sharp datasheet isn't what I would call straightforward, at least for the uninitiated (whom I count myself among). The power up sequence was pretty clear but once it came to pushing pixels it got a little vague. Really it was just a bunch of waves on the sheet.

One of the waves is a constant 5-60Hz pulse. That is the sort of thing that would be very irritating to create if you are bit banging on the main loop of your program, so I needed to get the AVR to pump that out in an automatic way. Researching the interwebz and reading the Atmega datasheet at length and comparing that to the output on the o-scope, I came up with this:

The prior code puts out a "phase correct" square wave on pin 11 at 60Hz. It also screws with pin 3 (not good) which I need to address next time I am at a scope. With that, it was just a matter of reading the data sheet for the screen and deciphering the thing into C code. I also found a non-arduino project on youtube using one of these screens and asked the poster to send me his source which was very helpful in understanding the datasheet. Once that was done, I converted that C code into C++ code and made a "SharpMemoryLCD" Arduino library. Currently it can print out basic strings and read byte[]s from PROGMEM and paste them to the screen. I will also add some other features like painting vectors to the screen and loading bitmaps from a disk before I'll call it "done". The current functionality is enough to get the reflow oven project I am working on finished though. That reflow oven project will be the basis of a future Freeside project/class where attendees will get a custom PCB and firmware to use to convert their toaster oven into a high quality reflow oven. You will be required to bring a 1500W toaster oven, and I think the rest of the stuff I'll include in the class fee (custom electronics, solid state relays, and thermocouples).

This is the code that produces the images in the video above. The library is not link up yet. I'll make a google code project for this once I have it a little more mature. Feel free to post up a comment if you want a pre-release copy. I'll hook you up.

During one of the last projects I was working on, I found that the first programming jig I made had a serious draw back. It could only put the #1 pin of the programmer in two of the four corners. That meant that I could only program my board from one side. That was fine until I assembled the project in it's case. At that point, reprogramming was a difficult task that required disassembly, something I never considered when I designed the item and as it turned out it was almost impossible to do without destroying it. Annoying!

Three weeks ago I decided I wanted to flash some new firmware on my motorcycle remote so I could use it to put a GPS on my Kindle Fire. That meant I needed take it apart and risk destroying it. Not an exciting prospect. Then I thought, why don't I just build another programming jig like the last one only upside down. That seemed like a winner, because it was fast, but I didn't have any more 2x3 ISP headers. Bah! Since I needed to wait on a shipment from Digikey I went ahead drew up a custom circuit board and added a few bells and whistles and sent it to fabricator.

The bells and whistles I spoke of are a pair of ISP headers which are mirror images of each other and a pair of LEDs that point to the #1 pin. When you plug into one the of the two headers, one of the two LEDs lights up pointing to the #1 pin. This function makes it easy to identify how to orient the PCB to the jig.

Below are images of the schematic and the board layout. The assembly is very easy. You just take two of the PCBs solder a pair of headers to the bottom board and pogo pegs to both and use some stand offs for strength. Check out the video for a better look at the final assembly.

Freesider's are evermore professional printistas of sorts. As our sprints are ramping up, there seems to be a growing interest in "organic modeling". Things often found in nature fall into this category for CAD artists.

Here is a recent Thingiverse upload, which was made from some very simple modeling techniques in Newtek's Lighwave 3D application. A little goes a very long way, indeed.

per Thingiverse.com:

There are 26 proper bones in the human foot; 28 if you consider the
sesamoids of the 1st metatarsal phalangeal joint complex. That's over
25% of your body's total musculo-skeletal anatomy, hitting the ground
every time you go for a walk or run! Quite impressive, really.

With the help of Freeside Atlanta Members, institutional researchers used open source Osirix Image viewer and 3D Software such as Newtek's Lightwave or Blender to create simulated surgical reductions as well as 3D printed templates. Freeside Atlanta members assisted in providing 3D printing solutions and know-how to the project.

Experimental test prints were done on a Makerbot Thing-o-matic, and final templates were printed on a modified ZCORP z400. These templates were full scale replicas of the patient's boney anatomy, which were used in the laboratory for practice purposes. (see video below)

The surgical bone cuts were trialed in advance and the the Ilizarov fixation frame was constructed and modified prior to surgery. The
combination of these two things saved the surgeons literally hours of
work in the operating theater, ultimately lowering cost of care and risk
of complications.

3D simulations were used for templating surgical approach on printed replicas.

Charcot foot syndrome (Charcot neuroarthropathy affecting the foot),
particularly in its latter stages, may pose a significant technical
challenge to the surgeon. Because of the lack of anatomic consistency,
preoperative planning with virtual and physical models of the foot could
improve the chances of achieving a predictable intraoperative result.
In this report, we describe the use of a novel, inexpensive,
3-dimensional template printing technique that can provide, with just a
normal printer, multiple "copies" of the foot to be repaired. Although
we depict this method as it pertains to repair of the Charcot foot, it
could also be used to plan and practice, or revise, 3-dimensional
surgical manipulations of other complex foot deformities.